The specific objective of this contract is to study the epidemiology and natural history of HIV infection in the heterosexually active population. The information generated by this contract is for the direct benefit and use of the Government in its efforts to describe the natural history of HIV infection among heterosexuals at risk for AIDS. Understanding the epidemiology of AIDS is an essential part of the overall effort to determine how to prevent or treat AIDS in the United States. Another contract shall be awarded for Part I to the Research Foundation of the State University of New York (SUNY) for the period 12/15/88-12/14/93, Contract No. N01-AI-95014. A contract shall be awarded to the University of Michigan, contract no. N01-AI-95015, for the Data Coordinating Center, Part II under this RFP for the same period of performance.